TreeWalker.currentNode

node = treeWalker.currentNode;
treeWalker.currentNode = node;

var treeWalker = document.createTreeWalker(
  document.body,
  NodeFilter.SHOW_ELEMENT,
  {
    acceptNode: function (node) {
      return NodeFilter.FILTER_ACCEPT;
    },
  },
  false,
);
root = treeWalker.currentNode; // l'élément racine car c'est le premier élément!